Methanogenisis is the last step in microbial biogas production. There are two groups of Methanogens, all of them are obligate anaerobes.

Bacteria can be grouped as aerobic or anaerobic based on their O2 requirement. Those with some tolerance are known as facultative and those very strict are the obligates. Based on metabolism, those that can utilizes carbohydrate for energy generation are saccharolytic while others that depends on other substrates are the asaccharolytic. The end products will of course vary from one group to another. In any ecosystem, the impact of these end products may change for example the pH of the environment and alter the ecosytem. 

is there a situation where asaccharolytic bacteria can contribute to deterioration of cell voltage if these bacteria are used for electricity production?

There also bacteria that are known as microaerophilic or microaerophiles.  The name denotes that they need micro amount of air for their growth such as Leptospira.

Aerobic bacteria usually use oxygen as terminal receptors of electrons from sugars and produce a lot of energy (ATP) through electron transport chain by oxidative phosphorylation, with end products of CO2 and water. When oxygen is depleted or absent, some bacteria can go into fermentation process where sugars are not completely oxidized and so only some electrons are extracted from sugars to make ATP with the end products of acids and alcohol.  In the absent of oxygen, anaerobic bacteria can use sugars as electron donor to make ATP but the bacteria still  need alternative electron receptors such as nitrate, nitrite, sulfate and some oxidative metal irons. When alternative electron receptors (eg., nitrate, sulfate, ferric irons) are absent, bacteria / archaea can even use CO2 as electron receptor to make energy from organic matter with end products of methane and water.